Feb 6th 1996.

We plan to attempt to turn the ASM on again on Feb. 20th. Full details on
the status of the ASM and the turn-on strategy are provided by
MIT .

Feb 2nd 1996.

The IOC period is now complete and we have transitioned to normal
observations. Hercules X-1 was one of the final IOC targets, the
observation was done at this time in order to observe at an appropriate
phase of the 35 day period exhibited by this system.

Monitoring observations of the TOO target GRO J1744-28 are continuing
and a short TOO observation of 4U1630-47 was also performed.

We will continue to provide information about XTE Science Operations on
this WWW page from time to time.

Jan 24th 1996.

We are now approaching the end of the main checkout period and are
preparing to concentrate on Guest Observer observations for AO1.
Schedules for these observations will be appearing on our Web pages in
the near future. A small number of calibration observations will be
done during the first week of AO1 observations. Throughout the lifetime
of the mission additional calibration observations will naturally also
be done from time to time as required.

An additional Target of Opportunity observation of the Galactic Center
transient source GRO J1744-28 is being planned for January 27th.

Jan 22th 1996.

Although we are still primarily carrying out calibration observations,
the first XTE GO observations from AO1 are now being done. Regular
monitoring of 3C 279 is currently being performed each day (proposal
number 10354) for 500 seconds. The short length of each observation
gives only a small impact on the calibration data.

Initial results from the XTE observation of GRO J1744-28 are reported
in IAU Circular number 6291. Additional information on XTE
Target of Opportunity observations is also available.

Jan 17th 1996.

Preparations are underway for tomorrow's observation of GRO J1744-28.
Due to the brightness of this source we currently intend to point at an
offset position in order to reduce the count rate to approximately
twice that of the Crab. This will reduce dead time effects in the PCA
caused by high count rates, especially during any bursts that may
occur. In order to determine an appropriate pointing position the
initial part of the observation will consist of a short series of scans
across what is thought to be the actual source location.

After an initial change at launch, the PCA gain now appears to be very
stable. This is consistent with our experience with this detector on
the ground. Also, with its automatic gain control enabled, the HEXTE
gain is stable to 0.25 %

Jan 16th 1996.

The first XTE observation specifically intended for science rather than
calibration purposes was performed today when the PCA and HEXTE
collected data on NGC 4945. As there is no pre-approved proposal to
observe this source the observation is public domain and the data will
be made available to the community on a similar timescale to other data
collected during the IOC period.

The next science target to be observed will be GRO J1744-28 with
observations scheduled to start late on January 18 and continue until
early on January 19.

Jan 15th 1996.

The PCA and HEXTE experiments continue to perform well and we are
accumulating additional calibration data.

It has been decided by the Project Scientist to perform a Target of
Opportunity observation of the Seyfert 2 galaxy NGC 4945 during the IOC
period (Jan. 16th). The decision to observe this source now was based
on factors which included the facts that GRO (OSSE) and ASCA
observations are currently being performed and that NGC 4945 is
presently known to be bright.

The ASM, however, has experienced additional problems. The (azimuthal)
ASM SSC2 experienced a high-count-rate turnoff on Friday night. It now
appears that the failures in both SSC3 and SSC2 are due to internal
high-voltage breakdown. One of the eight anodes was involved in SSC2
and two in SSC3. All other anodes appear to be unaffected. All three
SSCs will be turned off in the interim while the data are being
analyzed and possible recoveries are studied.

The ASM motor is still carrying out planned rotations and dwells and
the rotation readouts are being used to checkout rotation algorithms.
The sun-avoidance HV on-off commanding has been implemented and is in
the command load for the current week.

Jan 11th 1996.

While the "Blizzard of 1996" has caused delays in updating this Web
page XTE operations have continued in spite of the heavy snow. Members
of the XTE team living close to GSFC managed to make their way into
work but at least one person found themselves unexpectedly working a 36
hour shift until their replacement could arrive!

Targets that have now been observed by XTE also include SMC X-1, Cyg
X-2 and MCG8-11-11. Real time software clearly showed the expected
pulsations from SMC X-1 in the PCA data and off-line analysis indicates
QPO in the Cyg X-2 data. Initial results from observations designed to
measure instrument bore-sights show that the PCA and HEXTE are aligned
to better than a few arc minutes.

Two of the SSCs appear to be working very well and the drive assembly
is performing as expected. However, SSC 3 is having some problems which
are being investigated. In addition, we are finding that pointing an
SSC at the Sun causes a count rate which is high enough to switch off
that SSC. We are therefore modifying our daily command loads so as to
automatically turn off the high voltage supply to an SSC whenever the
Sun will be in the field of view of the instrument.

Our initial model of the SAA has proved to be somewhat over-optimistic
and we are now going to use a bigger region. Particle monitor data from
HEXTE is being utilized in order to find the best contour to use for
the SAA.

Upcoming observations include more pointings at MCG8-11-11, the Perseus
cluster, and additional observations of the Crab to provide better
information on dead time and instrument field of view.

Later in the month we also hope to be able to perform observations of
the recently discovered Galactic center transient source GRO J1744-28.

Jan 6th 1996.

Today the PCA and HEXTE made their first observations of cosmic X-ray
sources. First to be observed was the pulsar PSR 1509-58. Data were
first received while the source was occulted by the Earth and, as the
pulsar emerged from Earth occult, the increase in count rate as we
detected the source could easily be seen on our real time display of
the PCA light curve. Subsequent analysis clearly showed the presence
of pulsations and HEXTE was able to measure the spectrum of the the
pulsar out to beyond 60 keV.

Next to be observed was the Crab nebula. Initial analysis indicates
that we are seeing count rates close to what were predicted before
launch.

ASM scans were made and Sco X-1 was very obvious in real time data. The
galactic center region was also observed.

Tonight and tomorrow very heavy snow falls are predicted for the
Goddard area. However, we hope to be able to continue with satellite
operations and proceed with further calibrations using the Crab nebula
and our first observation of an AGN, MCG8-11-11.

Jan 5th 1996.

XTE has now made its first observations of X-ray sources! The high
voltages to the ASM SSCs were turned on with the detectors rotating for
several hours and a number of sources, including the Crab, were
detected. Complete information on source positions and fluxes awaits
calibration of detectors and verification of software.

The PCA and HEXTE detectors were also operated while viewing "empty"
positions on the sky and these experiments continue to perform with no
apparent problems.

We have now been given the go-ahead by the engineers to move to the
next stage of the checkout phase. The spacecraft will operate with
both high gain antennas (instead of one HGA and one omni antenna) and
the Virtual Recorder has been repartitioned so as to increase the ratio
of science to engineering data that is stored.

Extensive calibration observations can now proceed. The observations
planned for Jan. 6 are:

PSR 1509-58

2 spacecraft orbits to verify accuracy of the spacecraft clock

Crab nebula

4 orbits to investigate instrument dead time and energy response

Crab nebula

3 orbits offset from the Crab by 1 degree to characterize instrument
point spread function

Background

6 orbits with 5 separate pointing directions

The ASM will operate again and regions of the sky that are observed are
expected to include the Galactic center.

Jan 4th 1996.

An extensive series of test pulse generator (TPG) experiments was run
on the PCA with the EDS operating in both Standard Modes and using the
Good Xenon modes. Tests to characterize the pulse height and pulse
shape characteristics of HEXTE were also carried out. In preparation for
turning on the high voltages to the ASM additional monitoring of SSC
rotation was performed.

Tomorrow there will be an engineering meeting where it will be decided
whether the XTE spacecraft is ready to enter the next phase of check
out where the science instruments have priority.

Jan 3rd 1996.

All five proportional counter units of the PCA have now had high voltages
turned on simultaneously and run for several hours. The detectors appear to
be operating as predicted. The high voltage supplies to both HEXTE clusters
were turned on last night and are now expected to remain on for the rest of
the lifetime of XTE. Rotation tests of the ASM continue and no problems have
been found.

Jan 2nd 1996.

The emphasis on operating XTE has, so far, been on checking out the
spacecraft systems rather than the science instruments. As the
engineers complete their tests more time will be made available for
checking that the science instruments are working correctly and then
progressing to calibration observations.

As of today, high voltage has been turned on at normal operating levels
for three out of the five PCA proportional counter units and both HEXTE
clusters. Both instruments appear to be healthy and showing close to
expected behavior. HEXTE rocking tests have also been successful. The
ASM high voltage will be turned on later but the drive has been turned
on and the SSCs have been seen to rotate following the commanded plan.